The Future in Automotive Front Lighting

To combat these difficulties, there are several other types of buck-boost converters that mitigate some of these problems at the cost of extra components. The SEPIC converter shown on the previous page uses two inductors, or one coupled inductor and an extra capacitor, to create a buck-boost topology that provides continuous input current and discontinuous output current, as shown below. The SEPIC yields advantages similar to the boost while allowing for buck-boost operation. An additional benefit provided is capacitive isolation between input and output. This configuration allows for a shorted output condition that would destroy a boost converter and some buck-boost implementations. The major difficulty with a SEPIC is that the control dynamics are much more difficult, as it is a fourth-order control system (two inductors). Good PWM dimming relies on well-behaved dynamics, and at times the SEPIC can be a problem.

Ideal input and output current waveforms of the single-stage topologies.

One other interesting non-isolated buck-boost topology is the Cuk converter shown on the previous page. This is almost identical to the SEPIC, except that the output diode and inductor are in opposite positions. This configuration creates an inverted LED load, which isn't ideal given the available control ICs. However, it yields the benefit of continuous output current and continuous input current, as shown above, which is optimal considering the benefits we described previously. The dynamics are again difficult as in the SEPIC, which may or may not be desirable, depending on the performance specifications. In general, the SEPIC and the Cuk are more expensive than the floating buck-boost topology, but both offer clear benefits over the standard topology. As a note, all of the buck-boost options can be designed to have fairly similar system efficiency.

Looking at all of these single-stage topologies, one can quickly see the benefits of the two-stage topology. For instance, the two-stage design has the buck-boost capability, since the first stage can boost as high as necessary to always ensure that the second stage is bucking. Moreover, the boost and the buck topologies are far easier to work with and far more efficient than any of the buck-boost configurations. Of course, the system's input and output current are both continuous (the optimal case for EMC and dimming performance), and the buck converter can handle any fault conditions very easily. Finally, the two-stage system allows for a much better level of scalability.

Moving forward, not every design will necessitate a two-stage implementation, as the performance upgrade may not outweigh the need for a low-cost design. However, it seems that many manufacturers likely will move toward two-stage solutions more often to leverage platform developments and economy of scale. Ultimately, this helps drive prices of higher-end front lighting systems down, allowing the next-generation headlight to be available over a broader range of automobiles in the future.

James, this is a good overview of the desing choices for LED lighting. The ability to combine functions in one lighting unit are a great improvement. It should also offer new options that have not been thought of before.

I assume that although the control funcitons may be more complex, the available microcontroller circuitry should make it possible to implement.

Sounds like a really perfect application for those Digital Power microcontrollers, not only do you get the ability and flexibility of a uC for doing lighting/control tasks that have never been thought of, you can also implement the whole boost-buck, buck-boost, buck, boost, SEPIC, CUK, Flyback, Forward, etc... with just one chip. Microchip and Atmel are good places to start, and have many application notes.

While the general observations and comments are valid... Others are predicting the market in question (automotive) is going to be going though some changes. Changes that would impact assumptions being made.

- Change from 12(14)v system to higher voltages 36(42-48)v. reason: to get more power without impacting size / weight of system. Predicted before without happening. This time may happen because of expanded use of electrical systems in new vehicles has already taken place (hybrids, elect. based power steering, etc..)

- higher voltages with feedback system based on actual light output would negate much of the need for boosting (pre-regulation) on the lighting system. This would bypass the most of the effects of temperature, battery charge status and time on performance of the lighting system. Yea , this is complex also, but with complexity involving much lower power components.

James, I know you work for a semiconductor company, so ICs are a natural choice. But we're driving LEDs here. Why not just use groups of (say) 3 LEDs in series with a series resistor? The auto companies are fanatics about cost, and nothing could be cheaper than a simple resistor. No one has cared about headlight brightness variations with battery voltage in the past. The power used by headlights is insignificant compared to the other loads in a car.

I wrote NHTSA in the spring of 2011 asking them why they do not mandate constant headlight illumination on all North American Vehicles instead of DRL's. NHTSA responded with a 116 page document that basically said it was not "fuel efficient" to use full lighting 24/7 because of the load it pulled on the electrical system. So for you to say, "The power used by headlights is insignificant compared to the other loads in a car" would be a false statement if used in that manner. If NHTSA and the EPA both agree this load is enough to cause excessive loss of fuel mileage, then, in their minds, it IS significant!

My primary concern is safety and safety only. I could care less about the loss of fuel mileage for the use of constant headlights because the safety advantage greatly outweighs the difference in fuel savings. I would gladly give up one mile per gallon to be safe and for my children to be safe.....it's really not that big of a deal. In fact, both of my children turn on their lights every time they start their cars. It has become a natural reflex from day one, just like buckling their seatbelts.

Another concern I voiced with NHTSA, is that there is no taillight illumination with DRL's and some are actually so bright, that the vehicle operator thinks their headlamps are on. I see way too many people driving during the wee early morning hours and late afternoons with no headlights, and it isn't safe! One possible cause of this and another factor is the IP Cluster. On older vehicles, the cluster was never illuminated until the lights were turned on. The darkness inside the vehicle gave the driver an indication his lights weren't on, thus, triggering the reflex to pull out the switch. With newer vehicles, almost every IP cluster is being illuminated as soon as the vehicle is turned on. With this lighting inside the vehicle and the DRL brightness, most drivers think their lights are on, when in fact, they are driving down the road with or without DRL's and no taillights! Another factor is DRL brightness and the DRL being combined with the headlight bulb. Some DRL's are so bright that the vehicle operator cannot distinguish the difference between the headlight and the DRL's, thus thinking their lights are on. A good example of this would be the 1998 and 1999 Chevrolet Trucks, Tahoe and Suburban's. The DRL's are integrated into the headlight bulb and the brightness difference is barely distinguishable. DRL's should never be integrated into the headlight bulb. They should be a dedicated bulb placed in close proximity to the headlight, but not within, and the brightness should be at least, 50% dimmer.

With the new technology of LED's, these will draw less current on the electrical system and result in better fuel efficiency. My hope is that the auto industry, the EPA and NHTSA, will all agree that safety is a greater concern than fuel efficiency and LED's will help change our way of thinking for overall safety. Canada has already implemented full time DRL's and with this, anytime you turn on your windshield wipers, you lights come on. I say go ahead and mandate full time DRL's in North America and add taillight illumination. Remove the option to turn off your DRL's and make them automatic as soon as the vehicle is either started or is taken out of park.

Headlights use about 30-60 watts, regardless of whether they are tungsten, halogen, HID, or LED. There really isn't that much difference in power consumption between the best and the worst. There are of course significant differences in appearance, light levels, and cost; but not in power usage.

A car uses about 15 KW to move down the road at constant speed. That means the headlight's power usage is about half a percent of the total. The difference between the most and least efficient headlight is only going to be one quarter of one percent difference. That's a mighty slim improvement for lights that cost hundreds of dollars more.

My point was that going from a 90% efficient electronic DC/DC converter to a 70% resistor is even less signficant. It seems like a considerable increase in cost and complexity for an insignificant benefit.

On the fuel efficiency impact of daytime running lights: I *challenge* anyone to be able to measure the MPG impact on a statistically significant basis. It's "lost in the noise" and too low to detect!

If you want to save electrical energy in a car's electrical system, there is far more low-hanging fruit that would provide a lot more benefit for the buck. Use schottky diodes in the alternator. Use brushless DC motors instead of the ancient brushed motors. Design the electronics to draw micramps instead of milliamps.

Very good point about the previous predictions of higher voltages, Thinking J. Ten years ago, we were sick of hearing about the forthcoming arrival of 42V architectures. And where are they now? I would add, though, that hybrids an EVs have used higher voltages (upwards of 300V in many cases). But I agree with you that convntional IC engine-based vehicles will have 12V (14V) for some time to come.

The standards electrical machines and components are required to meet in the food processing industry are far more stringent than those in traditional plant construction. For specialized production environments such as these, components must not only resist thermal and physical stresses, but they must also be resistant to the chemicals used to sterilize equipment.

The word “smart” is becoming the dumbest word around. It has been applied to almost every device and system in our homes. In addition to smartphones and smart meters, we now hear about smart clothing and smart shoes, smart lights, smart homes, smart buildings, and every trendy city today has its smart city project. Just because it has a computer inside and is connected to the Web, does not mean it is smart.

Was Steve Job’s signature outfit of a black turtleneck, jeans, and sneakers the secret behind his success? Maybe, or maybe not, but it was likely an indication of a decision-making philosophy that enabled him to become one of the most successful innovators of all time.

Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.